Arthropods III. Insect diversity: wings, larvae and pupae Flashcards
Describe wings
- evolved once in the insects
- NOT segmental appendages with articles; evolved de novo
Describe termite wings
- only have wings at certain life history stages
- workers do not have wings
Describe parasitic lice wings
- lost
- complete life cycle on host
Describe the two theories for the origin of insect wings
- paranotal theory: wing develops from outgrowths of nota
- Endite-Exite theory: wing develops from exites of primitive leg segments
Describe the paranotal theory
- proto wing
- notum
- sternum
Describe the endite-exite theory
- sternum
- expicoxa
- proto wing
- subcoxa
- coxa
- exites
- prefemur
- femur
- tibia
Describe powered flight
- cycle of power and recovery stroke
- need angle change of wing, and up-down flapping
- edge of wing towards front of insect is leading edge
- veins made of cuticle for strengthening function
- actively generates lift
power stroke
down & forward
recovery stroke
up and backwards
Describe the innovation of powered flight
- only appeared four times in the history of life
- insects first (in mid-Carboniferous 330Mya)
- Pterosaurs in Triassic 225Mya
- Avialans in Jurassic 150Mya
- Bats in Tertiary 60Mya
Describe powered flight in the Paleoptera - the basics
- controlled by direct flight muscles
- e.g. dragonfly
Describe the direct flight muscles
- antagonistic muscles
- anterior and posterior direct muscles
antagonistic muscles
contract in turn to give cyclic movement
anterior and posterior direct muscles
control forward and backward movements
Describe the Paleopteran flight - the specifics
- elevator muscles pull wings up
- depressor muscles pull wings down
Describe powered flight in non-Paleopterans
- recovery stroke by indirect vertical flight muscles
- power stroke by indirect longitudinal flight muscles
- steering achieved by direct
muscles - sensors key to controlling flight
Describe the indirect vertical muscles
- pull on roof of thorax
- wings rise, thorax widens & lengthens
- stretches longitudinal muscles
Describe the indirect longitudinal muscles
- pull on anterior and posterior ends of thorax
- wings lower, thorax narrows and shortens
Describe the likely evolution of powered flight
- likely from gliding ancestor
- gliding generates lift through fixed angle, non- flapping wing or lobe
- hinge, venation, muscle and respiration adaptions needed for flapping flight in insects
- folding of wings in non- Paleopterans opened up habitat opportunities
- asynchronous muscle
evolved few times independently to increase wing beat frequency and allow a decrease in body size
Describe the Crematogaster ant
parachuting
Describe the Cephalotes ant
- gliding sensu lato
- directed aerial descent
- provided by glide angle
Describe the Draco lizard
- gliding sensu lato
- classic gliding controlled by drag and lift resultant forces
Flapping flight found in
hummingbird
Describe the advantages of wings and powered flight
- mobility: food, niche, habitat space (microhabitats)
- dispersal: competition & speciation
- predator avoidance
Powered flight is an evolutionary innovation that is
one reason for the huge diversity and abundance of insects
Describe Ametaboly
- no metamorphosis
- immature is a miniaturised version of adult
- 1% of species
Describe Hemimetaboly
- incomplete
metamorphosis - immature (nymph) is a miniaturised, wingless version of adult
- wings appear with new moults in late nymphs
- 16% of species
Describe Holometaboly
- complete
metamorphosis - immature (young larva) is very different from adult
- terminal larva
- larva transforms into pupa (quiescent stage)
- winged adult emerges from pupa
- 83% of species
Describe the metamorphosis of a locust
- hemimetaboly
- 1st-instar nymph has a pronotum and a coastal margin of hind wing
- 5th instar nymphe has pronotum, coastal margin, underside of hid wing, femur, tibia and tarsus
- adult locust has coastal margin and upper surface of fore wing
Describe the specifics of Holometabolous development
- adult form = imago
- metamorphosis during pupal
stage where larval organs are hydrolysed and reformed into adult organs - larvae moult several times to get larger during development, forming larval instars of different stages
Describe the evolution of holometaboly
- enigmatic
- pupae thought to be highly modified larval state
Give an example of a holometabolous species
silkworm (moth)
Describe the development and regulation of holometaboly
- hormonally controlled
- most adult structures develop from imaginal discs
imaginal discs
- clusters of embryonic reserve cells
- unique to holometabolous insects
Describe the advantages holometabolous development
- larvae and adults of holometabolous insects are ecologically very different
- mechanism to control speed of development
- diapause
- parasitoidism in four families of wasps and flies
Describe diapause
insects can pause development depending on environment (can be at any life stage)
Describe the importance of niche partitioning in metamorphosis
- allows specialisation to different niches (e.g. mouthparts)
- resource partitioning (e.g. different food sources)
- avoidance of competition between different life stages
- larvae for feeding and growth; adults for reproduction and dispersal
Describe parasitoidism
- larvae parasitoids on host
- adults free living (feed on nectar)
- smaller than host
- long term exposure
- association leads to host death
- every hexapod has its own parasitoid
- hyperparasitoids
- most important method for controlling insect populations
Describe wasp parasitoids
use ovipositor to lay eggs in host
Describe insect adaptations
- adaptations for a terrestrial existence
- co-evolution with angiosperms
- eusociality
How are insects adapted for terrestrial existence?
waxy cuticle, trachea & spiracles, hyperosmotic excreta
Describe eusociality
- Ants/Bees/Wasps, Termites & others
- Honeybees form eusocial colonies of close relatives
Describe insect coevolution with angiosperms
- phytophagous insects
- pollinators
Describe a phytophagous insect
Caterpillars produce enzymes to help them neutralise plant anti- herbivory toxins
